Processes for the hydrogenation of aromatic amines have long been known. Typically, hydrogenation processes involve contacting an aromatic amine with hydrogen in the presence of a transition metal catalyst. In the hydrogenation of single ring aromatic amines such as toluenediamine, rhodium, ruthenium, nickel and cobalt are the widely used catalysts.
A problem associated with processes involving the hydrogenation of aromatic amines is one of catalyst life. Not only are aromatic amines inherently difficult to hydrogenate, various impurities often are present in the aromatic amine feedstock which act as catalyst poisons. Toluenediamine, for example, is difficult to hydrogenate and the present of ortho-toluenediamine isomers exacerbates the problem. Rapid deactivation of the catalyst, e.g., rhodium is a consequence. To effect hydrogenation of aromatic amines, and single ring aromatic diamines in particular, purification of the feed material prior to hydrogenation often is required.
Representative patents that describe the hydrogenation of aromatic amines are as follow:
U.S. Pat. Nos., 2,511,028; 2,606,924; 2,606,925 and 2,606,928 describe a process that involve the hydrogenation of a purified methylene dianiline at pressures in excess of 200 psig, preferably in excess of 1,000 psig, at temperatures within the range of 800 to 275 xc2x0 C. utilizing a ruthenium catalyst. The hydrogenation is carried out in the presence of an inert organic solvent. Examples of ruthenium catalyst used in the hydrogenation process include ruthenium oxides, such as ruthenium sesquioxides and ruthenium dioxide; and ruthenium salts.
U.S Pat. Nos. 3,696,108 and 3,644,522 describe processes for the manufacture of PACM by hydrogenation methylenedianiline. The authors found that if the ruthenium was carried upon a support and the support was alkali-moderated, the catalyst was much more active and catalytically effective in producing the desired hydrogenated PACM product. Alkali moderation was effected by contacting the catalyst and support with alkali metal hydroxide of alkali oxide; also, such alkali moderation of the catalyst could be effected prior to hydrogenation or in situ during the hydrogenation.
U.S. Pat. No. 3,450,759 discloses a process for the hydrogenation of toluenediamine and the patentees note the difficulty of the reaction and the resulting low yields. They attributed low yields in the hydrogenation process to the presence of ortho-toluenediamines. Their improved process relied on removing ortho-toluenediamines from the feed prior to hydrogenation.
U.S. Pat. Nos. 4,754,070 and 4,946,998 relate to an improved process for the hydrogenation of methylene dianiline contaminated with oligomers and formaldehyde condensates to produce bis(para-aminocyclohexyl)methane (PACM). The inhibiting characteristics of the contaminates were overcome by contacting the crude methylenedianiline and hydrogen in the presence of a two component metal catalyst comprised of rhodium and ruthenium. Alkali moderation of the catalyst was also shown to be effective.
U.S. Pat. No. 5,973,207 relates to an improved process for the hydrogenation meta-toluenediamine by carrying out the hydrogenation in the presence of rhodium and a C3-C10 secondary alcohol as a solvent. Hydrogenation of meta-toluenediamine can be carried out on samples containing about 0.3% of o-toluenediamine isomers.
This invention relates to an improved process for the catalytic hydrogenation of aromatic amines, and particularly, a process for the catalytic hydrogenation of single ring aromatic diamines and specifically ortho-aromatic diamines. The basic process involves contacting the aromatic amine with hydrogen in the presence of a metal catalyst under conditions of hydrogenation in a reaction vessel. The improvement in the basic process resides in the steps comprising:
effecting the hydrogenation of the aromatic amine in the presence of a catalyst comprised of rhodium metal;
utilizing a C4-12 dialkyl ether as a solvent; and,
effecting delay addition of the aromatic diamine to the reaction medium. The level of unreacted aromatic amine in the reaction medium is, therefore, limited.
Significant advantages can be achieved by practicing the process and these include:
an ability to hydrogenate single ring aromatic diamines particularly ortho-aromatic diamines;
an ability to hydrogenate aromatic amines, e.g., ortho-aromatic diamines and particularly ortho-toluenediamines and achieve high selectivity; and,
an ability to hydrogenate such aromatic amines and achieve excellent reaction rates and catalyst life.
This invention relates to an improved process for the preparation of aromatic mines and preferably single ring aromatic diamines, such as toluenediamines, wherein the aromatic diamine is contacted with hydrogen in the presence of a rhodium hydrogenation catalyst. Specifically, the process is effective for the hydrogenation of ortho-toluenediamines to produce 1,2-diaminomethylcyclohexanes and the hydrogenation of meta-toluenediamines without effecting removal of contaminating impurities.
The aromatic amines include bridged and single ring versions. Bridged aromatic amines include methylenedianiline. The single ring aromatic amines which may be hydrogenated by this catalytic process include meta-toluenediamines, e.g., 2,4- and 2,6-meta-toluenediamines, ortho-toluenediamines, e.g., 2,3- and 3,4-ortho-toluenediamine, and ortho-, meta- and para-phenylene diamines. Typical products made by the process are 1,2-diamino-3-methyl-cyclohexane, 1,2-diamino-4-methyl-cyclohexane. Products that can be made by this process are: 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, 1,3-diamino-4-methyl-cyclohexane, 1,3-diamino-2-methyl-cyclohexane, 1,3-diamino-5-methyl-cyclohexane.
To effect hydrogenation of the aromatic amines, the hydrogenation catalyst is comprised of rhodium carried on a support. Other catalytic metals used in the hydrogenation process can be used in small amounts, e.g., up to about 10% by weight. Representative catalytic metals include ruthenium, palladium, nickel and cobalt. Representative supports include silica, alumina, e.g., kappa, delta, gamma and the like, titania, kielsulguhr and so forth. Typically, the rhodium is carried on the support in an amount of from 1 to 25 weight parts per 100 weight parts of support and preferably from 3 to 6 weight parts per 100 weight parts support.
To maintain high activity of the catalyst system in the hydrogenation process, it is preferred that the rhodium catalyst is alkali moderated. Alkali moderation typically involves the treatment of the catalyst and support material with an alkali metal hydroxide or alkali metal alkoxide, preferably lithium hydroxide or lithium ethoxide. Other alkali metals may be used, e.g., sodium and potassium but are not preferred. The alkali metal is added to provide from about 0.1 to 15% by weight of the rhodium metal including support. Often, moderation is done prior to reduction of the catalytic metal or following deposition of the rhodium on the support. Adding the alkali metal hydroxide to the reaction medium during the hydrogenation process may effect in situ alkali moderation.
Key to the hydrogenation process is the carrying out the hydrogenation in the presence of a C4-C12 dialkyl ether solvent. These solvents allow for liquid phase conditions to be maintained. Representative dialkyl ethers solvents suitable for practicing the invention include MTBE (methyl-teft-butyl ether), DEE (diethyl ether), THF (tetrahydrofuran), dioxanes, dioxolanes and so forth. Optionally, a small amount of other solvents can be used, e.g., from about 2 to 20 percent by weight of the total solvent used. Other solvents include aliphatic and alicyclic hydrocarbons. Examples include pentane, hexane, cyclohexane, methyl-cyclohexane, octane, cyclooctane and so forth.
The solvent is utilized in the hydrogenation process in an amount generally from about 10 to 80 weight percent of the amine introduced into the reaction vessel. Typically, the solvent is used at levels from about 50 to about 200 percent by weight of the aromatic amine, e.g., ortho-toluenediamine feed material.
Another key to the process is the use of semi-batch conditions. Under these conditions, the feed rate of the aromatic amine to the reactor vessel or the reaction medium contained in the reactor vessel is selected to match the rate of hydrogenation. In that way the contact time between the unreacted aromatic amine (ortho-diaminetolune) and the catalyst is minimized. The aromatic amine, e.g., ortho-toluenediamine is added to the reactor vessel at a rate of from about 0.02 to about 1.0 ml/min of OTD per gram of active catalyst including support, and preferably from about 0.06 to about 0.4 ml/min OTD per gram of active catalyst. The level of unreacted aromatic amine in the reaction medium should not exceed 1.5% by weight, and preferably should be within a range of from 0.1 to 0.8% by weight.
Temperatures for effecting hydrogenation range from about 130 to 220xc2x0 C. with preferred temperatures of from about 140 to 195xc2x0 C. Hydrogen partial pressures necessary for effecting hydrogenation of the aromatic amine feedstock range from about 500 to 4,000 psig, although modest pressures from 800 to 2,500 psig can be utilized.